It was estimated that approximately 150 million people worldwide had type 2 diabetes (T2D) in the year 2000, with the prediction that this number could double to 300 million by 2025 (1). T2D is characterized by insulin resistance in peripheral tissues and deficient β-cell insulin-secretory response to glucose. Glucose-sensing by pancreatic β-cell plays an important role in regulating glucose homeostasis and onset of T2D. Normal pancreatic β-cells are able to sense minor changes in blood glucose levels, and promptly respond to such changes by adjusting insulin secretion rates to maintain normoglycemia (2). In patients with insulin resistance, the pancreatic β-cells have to secret higher levels of insulin as a compensatory response to insulin resistance in order to maintain normoglycemia, resulting in hyperinsulinemia. Consequently, T2D develops only in subjects that are unable to sustain this β-cell compensatory response (3, 4). This is supported by results from longitudinal studies of subjects that develop T2D. These patients show a rise in insulin levels in the normoglycemic and prediabetes phases, followed by a decline in insulin secretion when β cells loss their ability to sense glucose, resulting pancreatic β cell failure and onset of diabetes (5). A longitudinal study in Pima Indians also confirmed that β-cell dysfunction was the major determinant of progression from normoglycemia to diabetes (6). Furthermore, the natural history of T2D entails progressive deterioration in β-cell function (7) and loss of β cell mass due to apoptosis (8, 9).
Current treatment options for type 2 diabetes include insulin, sulfonylureas, glitinides, acarbose, metformin, thiazolidinediones. These drugs lower blood glucose through diverse mechanisms of action. However, many of the drugs cannot prevent β-cell death or re-establish β-cell mass, and most of the oral hypoglycemic agents lose their efficacy over time, resulting in progressive deterioration in β-cell function and loss of glycemic control. Moreover, sulfonylurea therapy has been shown to induce apoptosis in rodent β-cells (10) or cultured human islets (11), thus likely exacerbating β-cell loss in T2D patients. Consequently, there has been intense interest in the development of therapeutic agents that preserve or restore functional β-cell mass (12). Several agents with the potential to inhibit β-cell apoptosis and/or increase β-cell mass have been identified in preclinical studies (12). One of the agents, a GLP-1 analogue, commercially known as Byetta (exenatide), has been shown to lower blood glucose level by improving β-cell function (β-15). Byetta is a peptide derived from the venom of the Gila monster, a poisonous lizard. Treatment of β-cell with Byetta has been shown to improve β-cell glucose sensing concurrent with preservation of β-cell mass and stimulation of β-cell regeneration (16). However, Byetta must be administered by injection twice daily, and long term usage of the drug has been associated with development of anti-exenatide antibodies in diabetic subjects. Additionally, the drug slows gastric emptying, and causes gastrointestinal discomfort.
Thus, there is a continuing need for compositions and methods for detection and treatment of diabetes in a subject. Further, development, of an oral antidiabetic drug that can improve glucose sensing by pancreatic β-cells is required for treatment of type 2 diabetes.